Lab-grown steaks nearing the menu

Fancy a beefburger, but want to spare the cow? Tissue engineers experimenting with ways of growing meat in a lab dish could soon provide a solution.

The aim of the work is to develop food for astronauts on long space journeys, such as a mission to Mars. But like much other space research, what happens up there could one day become commonplace down here too - just look what happened to Velcro.

A NASA-funded team led by Morris Benjaminson, at Touro College in New York City, has already taken the first steps. The team removed chunks of live muscle tissue from freshly killed goldfish and raised them in a standard cell-culture fluid for a week. The tissue grew by as much as 14 per cent, thanks to partially differentiated "myoblast" cells in the adult muscle dividing to make more muscle cells, he says.

But growing larger pieces of muscle tissue in the lab will be tricky. The main problem is ensuring a constant supply of nutrients for the growing cell mass. In a tissue fed by a blood supply, the capillaries must be no more than 200 microns apart or else the cells in between become necrotic and the tissue dies.

Although the Touro team developed techniques for growing white and dark chicken muscle in the lab, without a blood supply the chicken meat grew for just two months before it was dead in the dish. Benjaminson is now submitting another NASA proposal to investigate mechanical or electrical methods of stimulating blood vessel growth.

Protein spheres

However, you only need to establish a good blood supply if you want to grow thick slabs of muscle. Vladimir Mironov, director of the Shared Tissue Engineering Laboratory at the Medical University of South Carolina in Charleston has other ideas. His team thinks the meat of the future will be a processed food closer to a sausage or hamburger.

In a detailed project proposal to NASA, he sets out how to grow cells on protein spheres suspended in growth medium. These could then be harvested and made into nuggets or patties.

His starting cells will be myoblasts, which normally live at the edges of muscle fibres and help repair the muscles if they are damaged. They are better suited than embryonic stem cells, Mironov says, because they are already part of the way down the road to forming the desired cell type, rather than being totally undifferentiated.

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Unfortunately, myoblasts do have a big drawback - they cannot survive unless they can attach themselves to something, and this makes them harder to grow in a stock. To get around the problem, Mironov plans to mix the cells with tiny spheres of collagen protein and then keep them in suspension with the help of a machine called a microgravity bioreactor.

According to Mironov, the simplest meat to grow is seafood because the myoblasts can be coaxed to divide better, but "chicken is nice", he says. His dream is that we will eventually be able to grow and cook fresh sausage overnight at home in special machine, just like a home bread maker.

Food and exercise

Although processed meat is likely to become a reality before more traditional cuts, researchers have not given up the dream of growing the perfect filet mignon in the lab. Mironov, for one, has thought of other ways of getting around the blood supply problem.

He suggests using a bioreactor with a branching network of hundreds of tiny edible tubes that act like artificial capillaries to convey nutrients to the growing meat. But to satisfy those who crave the texture and mouthfeel of a good steak, you need to develop something that mimics the texture of real meat.

That means generating a complex structure of muscle and connective tissue, and to do that, the muscle myoblasts need to stretch and contract regularly. In other words, not only must you feed your steak well, you have to give it plenty of exercise too.

Herman Vandenburgh of Brown University has proposed a regime for the physical conditioning of sedentary steaks. Rather than just stimulating them with electricity or chemicals, Vandeburgh's team has developed chitin beads that change size when the temperature changes. When attached to the myoblasts, they force them to stretch and contract.

However, in a cruel setback for astronaut omnivores, NASA has rejected Mironov's proposal, apparently preferring astronauts to be vegetarians for the meantime. "People are vegetarians and vegans on Earth and they do quite well," comments Thomas Dreschel, director of NASA's Fundamental Biology Outreach Programme. "It is more efficient to grow plants and feed on them. If astronauts really need essential amino acids, they can eat a pill."

Select cut

But Douglas McFarland, at South Dakota State University in Brookings, who collaborates with Mironov, disagrees. "Animal protein is a more balanced and complex protein than a plant protein," he argues. "The body would absorb and metabolise protein from a pill too rapidly. If you eat protein, then it takes more time to digest."

Even if NASA is focusing on veggies, maybe Mironov can find funding elsewhere. "Operations like McDonald's are interested in particular cuts of meat and efficiency," says Vern Anderson, adjunct professor of ruminant nutrition at the University of North Dakota. "And you could select for leanness, or low cholesterol."

Gaining general consumer acceptance of such meat might be possible if it tasted good. But the reaction of vegetarians and animal rights campaigners is another matter. If no animal is farmed or slaughtered, and if culturing cells were more energy efficient than growing meat on the hoof, would that make it ethically acceptable?

If not, there might still be another way. One researcher recalls a student, a vegan, who asked if she could just biopsy herself, grow up a steak and eat it. If you want to eat truly victimless meat, perhaps it is time to put yourself on the menu.

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